Facebook’s network of 58 million active users and its status as the sixth-most-trafficked Web site in the United States have made it an irresistible subject for many types of academic research. Scholars at Carnegie Mellon used the site to look at privacy issues. Researchers at the University of Colorado analyzed how Facebook instantly disseminated details about the Virginia Tech shootings in April. But it is Facebook’s role as a petri dish for the social sciences — sociology, psychology and political science — that particularly excites some scholars, because the site lets them examine how people, especially young people, are connected to one another, something few data sets offer, the scholars say. Social scientists at Indiana, Northwestern, Pennsylvania State, Tufts, the University of Texas and other institutions are mining Facebook to test traditional theories in their fields about relationships, identity, self-esteem, popularity, collective action, race and political engagement. Much of the research is continuing and has not been published, so findings are preliminary. In a few studies, the Facebook users do not know they are being examined. A spokeswoman for Facebook says the site has no policy prohibiting scholars from studying profiles of users who have not activated certain privacy settings. Although federal rules govern academic study of human subjects, universities, which approve professors’ research methods, have different interpretations of the guidelines. “The rules were made for a different world, a pre-Facebook world,” said Samuel D. Gosling, an associate professor of psychology at the University of Texas, Austin, who uses Facebook to explore perception and identity. “There is a rule that you are allowed to observe public behavior, but it’s not clear if online behavior is public or not.”